text: #include "stm32f4xx_hal.h"
  
  extern UART_HandleTypeDef huart3;
  
  int _write(int fd, char *str, int len)
  {
  	int ret;
  
  	if (fd != 1) return -1;
  
  	ret = HAL_UART_Transmit(&huart3, (uint8_t *)str, len, 0xFF);
  	if (ret < 0) return -1;
  
  	return len;
  }
  